This invention concerns optical and optronic systems for proximity detection.
Such detectors already exist; they are fitted to weapons or missiles, and their function is to trigger the detonation of the weapon, or of a warhead carried by the missile, when the weapon or missile "nears" a target.
To this end, known detectors include a window, fitted to the nose cone or the body of the weapon. This window is transparent to a predetermined range of frequencies; an optical device enables surveillance of an angle of observation .THETA. relative to the longitudinal axis XX' of the missile or weapon. The angle 8 is generally slightly less than 90.degree.. The optical device enables radiation to be captured in a solid rotational angle around the axis of the missile or weapon.
Radiation given off by the target in the solid angle determined by the optical input is reflected by a mirror towards a detector. This is illustrated in FIGS. 1, 2, and 3.
FIG. 1 shows a missile (1) which carries a detector window (2). The bisecting axis of a cross-section of the field makes an angle .THETA. of a little less than 90.degree. with the longitudinal axis XX' of the missile. The bisecting axes on either side of the axis of symmetry of the missile or projectile meet at point 0. The angle of opening of this window is 2.tau.. The window enables the capture of radiation coming from any point within a rotational volume bounded by two surfaces. The first of these surfaces is a rotational cone with its apex at a point 0', which is set slightly ahead of point 0. The generator of the cone is a straight line set at an angle (.THETA.-.tau.) to axis XX'. The second of these surfaces is a rotational cone with its apex at a point 0", which is situated slightly behind point 0. The generator of the second cone is a straight line set at an angle (.THETA.+.tau.) to the axis of rotation of the missile.
FIG. 2 shows a simplified diagram of missile (1) approaching a target (3), which is represented by a triangle. Target (3) includes a hot spot (4).
FIG. 3 shows a ray (5) coming from the hot spot (4) in FIG. 2 and entering the missile through the window (2). This ray is reflected by a 360.degree. mirror (6) symmetric about the missile axis, towards a detector (7) which is sensitive to the radiation given off by the hot spot (4). Upon sensing the radiation, the detector emits a signal which is amplified and processed to trigger the detonation of a warhead whose zone of influence is rotationally symmetric about axis XX'.
As has been illustrated, existing passive optronic detectors do not detect the "nearness" of the target, but only its transit.
The highest degree of proximity between the target and the missile is often reached at the moment when the missile crosses the target; this is particularly noticeable when the target and the missile have convergent trajectories. When the trajectories are not convergent, the transit may not be the point of closest proximity between target and missile; this is particularly true of highly maneuverable missiles. Moreover, captured radiation may originate from a distant source lying within the volume of detection; such a source may be a target other than the one under pursuit an individual lure, or the sun--if the detector is sensitive to the radiation of such bodies.
Furthermore, existing detectors sense the crosswise motion of the target, but they do not enable determination of the precise solid angular sector containing the target. These deficiencies necessitate the use of a warhead with an efficient volume rotationally symmetric about axis XX' of the projectile. For the same mass, a directed-effect warhead in the direction of the target would have significantly greater efficiency.
Finally, due to their design, existing systems require a detector (7) to be placed towards the front of the missile.
This may make it more difficult to integrate any possible detector cooling system.
Signal-processing systems can be located elsewhere, insofar as this is allowed by the low level of signals generated by the detectors; however, it then becomes necessary to use available volume for connections and the cables carrying signals. This must be set against the fact that in a weapon, the goal is to reduce the weight and volume of anything other than the warhead.